Craniectomies requiring cranioplasty are either decompressive following stroke/trauma or occur as a result of oncological ablation for masses involving the bony calvarium. In the setting of trauma with cerebral edema, stroke with bleeding, or autologous bone flap osteomyelitic infections requiring removal, delayed cranioplasties are necessary at a secondary stage. In fact, nearly 250,000 primary brain tumors/skull-based neoplasms are diagnosed each year resulting in a range of 4500-5000 second-stage implant cranioplasties/year.
Craniectomy defects following resection of calvarial lesions are most often reconstructed using on-table manufacturing, similar to all defects in the craniomaxillofacial skeleton. For tumor ablative surgery—where tumors and/or processes involve the bony calvarium—cranioplasties are most often performed primarily using suboptimal hand-molding techniques. Currently, the standard of care is to reconstruct the cranial defects with on-table manipulation using a varying combination of materials. For example, oncological defects are commonly reconstructed with “off-the-shelf” materials, as opposed to using a pre-fabricated customized implant simply because the exact defect size/shape is unknown. As a result, a variety of materials may be used to reconstruct large cranial defects, including titanium mesh, porous hydroxyapatite (HA), polymethylmethacrylate (PMMA), and polyether ether ketone (PEEK), among others.
Some of these materials can be molded and/or shaped in the operating room to approximate complex, three-dimensional defects, especially in instances greater than 5 cm squared in size. Of note, the most frequently used material next to titanium mesh is liquid PMMA, which is used alone for small defects and/or in conjunction with titanium mesh for larger defects. It is affordable, time-tested and easy to use. However, on-table manipulation often results in some form of craniofacial asymmetry and a post-operative appearance which is suboptimal. Furthermore, the difficult shaping process may take significant time (i.e., up to 80 minutes), which in turn increases anesthesia, total blood loss, risk for infection, morbidity, and all costs associated with longer operative times. In addition, titanium mesh onlay reconstruction—which is one of the most common methods currently utilized—requires overlapping and therefore its sharp, irregular edges may easily extrude and/or pierce the scalp over time, especially in the setting of post-operative irradiation.
With the advent of computer-aided design/manufacturing (CAD/CAM) and customized craniofacial implants (CCIs), more suited alternatives are becoming available. With CAD/CAM fabrication, near-perfectly shaped CCIs can be ordered and pre-fabricated based on fine cut preoperative computed tomography (CT) scans and three-dimensional reconstruction (+/−stereolithographic models). In fact, recent reports suggest that CCI's have the ability to improve cosmesis, decrease operative times and enhance patient satisfaction, if altered for exact reconstruction in real-time during “single-stage” cranioplasty reconstruction.”
For example, preoperative imaging such as CT may be used to identify the patient anatomy ahead of time, but the exact defect size following tumor resection is unknown. To follow true oncological principles and to make sure the surgeon is unrestricted in removing all concerning areas of disease (thereby decreasing all risk of recurrence), the prefabricated implant must be able to accommodate the unexpected three-dimensional defect and size, rather than the defect accommodating the prefabricated implant with use of a cutting guide; this is currently being done as a suboptimal solution. As such, the pre-operative CT scan images are used to virtually plan the surgical cuts in an oversized area around the skeletal tumor with excess of several centimeters based on exact location and to allow the geometric design of the three-dimensional (3D) CCI to be created in an “oversized” fashion”. In so-called “single-stage cranioplasty”, the pre-fabricated custom implant with excess dimensions is designed to account for any additional bone/soft tissue that may become necessary to remove during the surgery (i.e., due to unanticipated local invasion, desire to decrease risk of recurrence and enlargement of resection limits, an unknown tumor pathology grade until resected and sent for frozen analysis with pathology, etc.). Therefore, after resecting the bony/soft tissue region of interest, the surgeon is forced to shave down and modify the oversized CCI to fit exactly within the resected area. However, this type of real-time, intraoperative, manual modification of the oversized custom implant is altogether “labor-intensive”, “technically-demanding”, and “time-consuming,” and is still not perfect for fitting when modified by hand-eye calibration.
Thus, CAD/CAM technology adds another dimension to the material chosen for reconstruction, for example, by allowing one to match the contralateral, non-operated side for ideal contour and appearance. Yet, in the literature, there are only a few case reports where immediate reconstructions with CCI's have been performed for benign skull neoplasms following resection (i.e., meningioma, fibrous dysplasia). While these isolated case reports have reported favorable results and acceptable outcomes, there is a trend towards decreased operative times, and less overall surgery by avoiding risk for revision surgery. In cases of malignant neoplasms involving the bony calvarium, secondary cranioplasty (after surgical margins have been cleared) is currently advocated. However, as of 2014, there was only one successful case report of immediate CCI reconstruction following resection of a Ewing sarcoma.
Historically, cranioplasties with such CCIs can only be performed as second stage operations during which a clinician, such as a surgeon, ensures that the CCI fits perfectly into the skull defect. The recent developments by the inventors and others have demonstrated the feasibility of CCIs for “single-stage cranioplasty”, but this involves using a handheld bur to shave down the pre-fabricated implant artistically. However, as described above, challenges in both assessing and predicting each tumor-resection deformity pre-surgery still limits the applicability of CCIs in this patient population. For example, challenges such as 1) unknown exact tumor size, 2) unknown growth from time of pre-op CT scan-to-actual day of surgery, and 3) the amount of unknown resection margins needed to minimize local recurrence. For these cases, the CCI would need to be reshaped/resized intraoperatively in real-time from a size slightly larger than expected; this process may take between 10-80 minutes.
Accordingly, use of a computer-assisted surgical system of an embodiment and a robot/cutting machine for implant modification may significantly reduce the intraoperative time used for reshaping/resizing the customized implant. However, with no established planning/execution systems and/or robots available to assist these single-stage reconstructions, a technology and/or surgical method that allows surgeons to resize, adjust, modify or trim alloplastic or bio-engineered implants during surgery to fit the surgical cuts, defects, and/or pre-existing deformities requiring complex reconstruction, or generally overcome the limitations of current technology and surgical methods, would be welcome in the art.